High-speed triple string drilling system

Abstract

A drilling system for boring into ground includes a bottom hole assembly having a rotatable casing shoe, an independently rotatable driveshaft disposed within the casing shoe, and a bearing housing interdisposed between the driveshaft and the casing shoe to control a distance between a centerline of the driveshaft and a centerline of the casing shoe. The driveshaft includes a bit disposed at a distal end thereof, extending beyond the casing shoe distal end. The driveshaft centerline and the casing shoe centerline are substantially parallel and radially offset.

What is claimed is: 
     
       1. A drilling system for boring into ground, the drilling system comprising a bottom hole assembly comprising:
 a rotatable casing shoe comprising a distal end; 
 an independently rotatable driveshaft disposed within the casing shoe, the driveshaft comprising a bit disposed at a distal end thereof extending beyond the casing shoe distal end; 
 a bearing housing interdisposed between the driveshaft and the casing shoe to control a distance between a centerline of the driveshaft and a centerline of the casing shoe, wherein the driveshaft centerline and the casing shoe centerline are substantially parallel and radially offset; and 
 a drill string assembly coupled to the bottom hole assembly, the drill string assembly comprising:
 an outer drill string coupled to the casing shoe; 
 an inner drill string disposed within the outer drill string and coupled to the driveshaft, the inner drill string forming an interior passage; and 
 an intermediate drill string interdisposed between the outer drill string and the inner drill string, the intermediate drill string coupled to the bearing housing. 
 
 
     
     
       2. The drilling system of  claim 1 , wherein the casing shoe comprises a cutter at a distal end thereof. 
     
     
       3. The drilling system of  claim 1 , wherein at least one of the casing shoe and the bearing housing define an internal passage to permit drilling fluid and any cuttings to be conveyed away from a cutting zone toward a proximal end of the casing shoe. 
     
     
       4. The drilling system of  claim 1 , wherein the driveshaft comprises tubing forming an internal passage adapted to direct drilling fluid to the bit. 
     
     
       5. The drilling system of  claim 1 , wherein the bearing housing is adapted to be rotationally locked with the casing shoe. 
     
     
       6. The drilling system of  claim 5 , wherein the bearing housing is axially translatable relative to the casing shoe between a retracted disengaged position to an extended engaged position. 
     
     
       7. The drilling system of  claim 6 , wherein the bearing housing comprises a projection adapted to mate with an aperture formed in the casing shoe. 
     
     
       8. The drilling system of  claim 7 , wherein the projection comprises a pair of wings and the aperture comprises a corresponding pair of longitudinally disposed slots. 
     
     
       9. The drilling system of  claim 8 , wherein the slots are canted circumferentially. 
     
     
       10. The drilling system of  claim 1 , wherein the bearing housing is adapted to rotate with respect to the casing shoe. 
     
     
       11. The drilling system of  claim 10 , wherein the bearing housing forms an offset bore to support the driveshaft and comprises a radial support adapted to mate positively with an internal surface of the casing shoe. 
     
     
       12. The drilling system of  claim 11 , wherein the casing shoe comprises an axial stop adapted to limit axial advancement of the bearing housing with respect to the casing shoe. 
     
     
       13. The drilling system of  claim 1 , wherein at least one of the casing shoe, the driveshaft, and the bearing housing are adapted to be translated longitudinally relative to at least one other. 
     
     
       14. The drilling system of  claim 1 , wherein each of the casing shoe, the driveshaft, and the bearing housing are adapted to be translated longitudinally relative to each other. 
     
     
       15. The drilling system of  claim 1 , further comprising a surface assembly, the surface assembly comprising:
 a drive assembly comprising:
 an outer drive unit coupled to the outer drill string; 
 an inner drive unit coupled to the inner drill string; and 
 an intermediate drive unit coupled to the intermediate drill string; and 
 
 a pump assembly comprising:
 an outer pump adapted to pump an outer fluid between ground and the outer drill string; 
 an inner pump adapted to pump an inner fluid through the interior passage of the inner drill string; and 
 an intermediate pump adapted to pump an intermediate fluid through an annular space formed between the intermediate drill string and the inner drill string. 
 
 
     
     
       16. The drilling system of  claim 15 , wherein the outer drive unit is adapted to rotate the casing shoe relative to ground. 
     
     
       17. The drilling system of  claim 15 , wherein the outer drive unit is adapted to longitudinally translate the casing shoe relative to ground. 
     
     
       18. The drilling system of  claim 15 , wherein the inner drive unit is adapted to rotate the driveshaft relative to ground. 
     
     
       19. The drilling system of  claim 15 , wherein the inner drive unit is adapted to longitudinally translate the driveshaft relative to ground. 
     
     
       20. The drilling system of  claim 15 , wherein the intermediate drive unit is adapted to rotate the bearing housing relative to ground. 
     
     
       21. The drilling system of  claim 15 , wherein the intermediate drive unit is adapted to longitudinally translate the bearing housing relative to ground. 
     
     
       22. The drilling system of  claim 15 , wherein each of the outer drive unit, the inner drive unit, and the intermediate drive unit is adapted to be locked to at least one of ground and another drive unit. 
     
     
       23. The drilling system of  claim 15 , wherein the drive assembly further comprises a second outer drive unit coupled to the outer drill string. 
     
     
       24. The drilling system of  claim 15 , wherein the outer fluid, the inner fluid, and the intermediate fluid each comprise at least one member selected from the group consisting of water, brine, lubricant drilling mud, viscous drilling mud, and weighted drilling mud. 
     
     
       25. The drilling system of  claim 24 , wherein at least one of the outer fluid, the inner fluid, and the intermediate fluid comprises a gaseous component. 
     
     
       26. The drilling system of  claim 1 , wherein the inner drill string comprises a wide portion and the intermediate drill string comprises a narrow portion to prevent the inner drill string from dropping through the intermediate drill string. 
     
     
       27. A method for boring into ground, the method comprising the steps of:
 orbiting and advancing into the ground a high speed rotating bit mounted to a driveshaft to form a bore having a nominal diameter; 
 following the bit with a casing shoe independently rotating at lower speed and having a diameter substantially equivalent to the nominal diameter; and 
 controlling a distance between a centerline of the driveshaft and a centerline of the casing shoe with a bearing housing interdisposed between the driveshaft and the casing shoe, such that the driveshaft centerline and the casing shoe centerline are substantially parallel and radially offset, wherein
 (i) an outer drill string is coupled to the casing shoe; 
 (ii) an inner drill string is disposed within the outer drill string and coupled to the driveshaft, the inner drill string forming an interior passage; and 
 (iii) an intermediate drill string is interdisposed between the outer drill string and the inner drill string, the intermediate drill string is coupled to the bearing housing. 
 
 
     
     
       28. The method of  claim 27 , wherein the controlling step comprises adjusting the distance between the centerline of the driveshaft and the centerline of the casing shoe by longitudinally translating the bearing housing. 
     
     
       29. The method of  claim 27 , wherein the controlling step comprises adjusting the distance between the centerline of the driveshaft and the centerline of the casing shoe by rotating the bearing housing. 
     
     
       30. The method of  claim 27 , further comprising:
 pumping an inner fluid through the interior passage of the inner drill string; 
 pumping an intermediate fluid through a first annulus between the inner drill string and the intermediate drill string; and 
 pumping an outer fluid through a second annulus between the bore and the outer drill string.